/* 基础样式 */
div, span, body, ul, li, p, a, address, em, strong, i {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

.mt10 {
  margin-top: 10px;
}

.mt {
  margin-top: 20px;
}

.mb {
  margin-bottom: 50px;
}

.ctmd {
  display: flex;
  justify-content: center;
  align-items: center;
}